/**
 * @file
 * Packet buffer management
 *
 * Packets are built from the pbuf data structure. It supports dynamic
 * memory allocation for packet contents or can reference externally
 * managed packet contents both in RAM and ROM. Quick allocation for
 * incoming packets is provided through pools with fixed sized pbufs.
 *
 * A packet may span over multiple pbufs, chained as a singly linked
 * list. This is called a "pbuf chain".
 *
 * Multiple packets may be queued, also using this singly linked list.
 * This is called a "packet queue".
 *
 * So, a packet queue consists of one or more pbuf chains, each of
 * which consist of one or more pbufs. CURRENTLY, PACKET QUEUES ARE
 * NOT SUPPORTED!!! Use helper structs to queue multiple packets.
 *
 * The differences between a pbuf chain and a packet queue are very
 * precise but subtle.
 *
 * The last pbuf of a packet has a ->tot_len field that equals the
 * ->len field. It can be found by traversing the list. If the last
 * pbuf of a packet has a ->next field other than NULL, more packets
 * are on the queue.
 *
 * Therefore, looping through a pbuf of a single packet, has an
 * loop end condition (tot_len == p->len), NOT (next == NULL).
 */

/*
 * Copyright (c) 2001-2004 Swedish Institute of Computer Science.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
 * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
 * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
 * OF SUCH DAMAGE.
 *
 * This file is part of the lwIP TCP/IP stack.
 *
 * Author: Adam Dunkels <adam@sics.se>
 *
 */

#include "lwip/opt.h"

#include "lwip/stats.h"
#include "lwip/def.h"
#include "lwip/mem.h"
#include "lwip/memp.h"
#include "lwip/pbuf.h"
#include "lwip/sys.h"
#include "arch/perf.h"
#if TCP_QUEUE_OOSEQ
	#include "lwip/tcp.h"
#endif

#include <string.h>

#define SIZEOF_STRUCT_PBUF        LWIP_MEM_ALIGN_SIZE(sizeof(struct pbuf))
/* Since the pool is created in memp, PBUF_POOL_BUFSIZE will be automatically
   aligned there. Therefore, PBUF_POOL_BUFSIZE_ALIGNED can be used here. */
#define PBUF_POOL_BUFSIZE_ALIGNED LWIP_MEM_ALIGN_SIZE(PBUF_POOL_BUFSIZE)

#if !TCP_QUEUE_OOSEQ || NO_SYS
#define PBUF_POOL_IS_EMPTY()
#else /* !TCP_QUEUE_OOSEQ || NO_SYS */
/** Define this to 0 to prevent freeing ooseq pbufs when the PBUF_POOL is empty */
#ifndef PBUF_POOL_FREE_OOSEQ
	#define PBUF_POOL_FREE_OOSEQ 1
#endif /* PBUF_POOL_FREE_OOSEQ */

#if PBUF_POOL_FREE_OOSEQ
#include "lwip/tcpip.h"
#define PBUF_POOL_IS_EMPTY() pbuf_pool_is_empty()
static u8_t pbuf_free_ooseq_queued;
/**
 * Attempt to reclaim some memory from queued out-of-sequence TCP segments
 * if we run out of pool pbufs. It's better to give priority to new packets
 * if we're running out.
 *
 * This must be done in the correct thread context therefore this function
 * can only be used with NO_SYS=0 and through tcpip_callback.
 */
static void
pbuf_free_ooseq(void* arg)
{
	struct tcp_pcb* pcb;
	SYS_ARCH_DECL_PROTECT(old_level);
	LWIP_UNUSED_ARG(arg);

	SYS_ARCH_PROTECT(old_level);
	pbuf_free_ooseq_queued = 0;
	SYS_ARCH_UNPROTECT(old_level);

	for(pcb = tcp_active_pcbs; NULL != pcb; pcb = pcb->next) {
		if(NULL != pcb->ooseq) {
			/** Free the ooseq pbufs of one PCB only */
			LWIP_DEBUGF(PBUF_DEBUG | LWIP_DBG_TRACE, ("pbuf_free_ooseq: freeing out-of-sequence pbufs\n"));
			tcp_segs_free(pcb->ooseq);
			pcb->ooseq = NULL;
			return;
		}
	}
}

/** Queue a call to pbuf_free_ooseq if not already queued. */
static void
pbuf_pool_is_empty(void)
{
	u8_t queued;
	SYS_ARCH_DECL_PROTECT(old_level);

	SYS_ARCH_PROTECT(old_level);
	queued = pbuf_free_ooseq_queued;
	pbuf_free_ooseq_queued = 1;
	SYS_ARCH_UNPROTECT(old_level);

	if(!queued) {
		/* queue a call to pbuf_free_ooseq if not already queued */
		if(tcpip_callback_with_block(pbuf_free_ooseq, NULL, 0) != ERR_OK) {
			SYS_ARCH_PROTECT(old_level);
			pbuf_free_ooseq_queued = 0;
			SYS_ARCH_UNPROTECT(old_level);
		}
	}
}
#endif /* PBUF_POOL_FREE_OOSEQ */
#endif /* !TCP_QUEUE_OOSEQ || NO_SYS */

/**
 * Allocates a pbuf of the given type (possibly a chain for PBUF_POOL type).
 *
 * The actual memory allocated for the pbuf is determined by the
 * layer at which the pbuf is allocated and the requested size
 * (from the size parameter).
 *
 * @param layer flag to define header size
 * @param length size of the pbuf's payload
 * @param type this parameter decides how and where the pbuf
 * should be allocated as follows:
 *
 * - PBUF_RAM: buffer memory for pbuf is allocated as one large
 *             chunk. This includes protocol headers as well.
 * - PBUF_ROM: no buffer memory is allocated for the pbuf, even for
 *             protocol headers. Additional headers must be prepended
 *             by allocating another pbuf and chain in to the front of
 *             the ROM pbuf. It is assumed that the memory used is really
 *             similar to ROM in that it is immutable and will not be
 *             changed. Memory which is dynamic should generally not
 *             be attached to PBUF_ROM pbufs. Use PBUF_REF instead.
 * - PBUF_REF: no buffer memory is allocated for the pbuf, even for
 *             protocol headers. It is assumed that the pbuf is only
 *             being used in a single thread. If the pbuf gets queued,
 *             then pbuf_take should be called to copy the buffer.
 * - PBUF_POOL: the pbuf is allocated as a pbuf chain, with pbufs from
 *              the pbuf pool that is allocated during pbuf_init().
 *
 * @return the allocated pbuf. If multiple pbufs where allocated, this
 * is the first pbuf of a pbuf chain.
 */
struct pbuf*
pbuf_alloc(pbuf_layer layer, u16_t length, pbuf_type type)
{
	struct pbuf* p, *q, *r;
	u16_t offset;
	s32_t rem_len; /* remaining length */
	LWIP_DEBUGF(PBUF_DEBUG | LWIP_DBG_TRACE, ("pbuf_alloc(length=%"U16_F")\n", length));

	/* determine header offset */
	offset = 0;

	switch(layer) {
		case PBUF_TRANSPORT:
			/* add room for transport (often TCP) layer header */
			offset += PBUF_TRANSPORT_HLEN;

		/* FALLTHROUGH */
		case PBUF_IP:
			/* add room for IP layer header */
			offset += PBUF_IP_HLEN;

		/* FALLTHROUGH */
		case PBUF_LINK:
			/* add room for link layer header */
			offset += PBUF_LINK_HLEN;
			break;

		case PBUF_RAW:
			break;

		default:
			LWIP_ASSERT("pbuf_alloc: bad pbuf layer", 0);
			return NULL;
	}

	switch(type) {
		case PBUF_POOL:
			/* allocate head of pbuf chain into p */
			p = memp_malloc(MEMP_PBUF_POOL);
			LWIP_DEBUGF(PBUF_DEBUG | LWIP_DBG_TRACE, ("pbuf_alloc: allocated pbuf %p\n", (void*)p));

			if(p == NULL) {
				PBUF_POOL_IS_EMPTY();
				return NULL;
			}

			p->type = type;
			p->next = NULL;

			/* make the payload pointer point 'offset' bytes into pbuf data memory */
			p->payload = LWIP_MEM_ALIGN((void*)((u8_t*)p + (SIZEOF_STRUCT_PBUF + offset)));
			LWIP_ASSERT("pbuf_alloc: pbuf p->payload properly aligned",
			            ((mem_ptr_t)p->payload % MEM_ALIGNMENT) == 0);
			/* the total length of the pbuf chain is the requested size */
			p->tot_len = length;
			/* set the length of the first pbuf in the chain */
			p->len = LWIP_MIN(length, PBUF_POOL_BUFSIZE_ALIGNED - LWIP_MEM_ALIGN_SIZE(offset));
			LWIP_ASSERT("check p->payload + p->len does not overflow pbuf",
			            ((u8_t*)p->payload + p->len <=
			             (u8_t*)p + SIZEOF_STRUCT_PBUF + PBUF_POOL_BUFSIZE_ALIGNED));
			LWIP_ASSERT("PBUF_POOL_BUFSIZE must be bigger than MEM_ALIGNMENT",
			            (PBUF_POOL_BUFSIZE_ALIGNED - LWIP_MEM_ALIGN_SIZE(offset)) > 0);
			/* set reference count (needed here in case we fail) */
			p->ref = 1;

			/* now allocate the tail of the pbuf chain */

			/* remember first pbuf for linkage in next iteration */
			r = p;
			/* remaining length to be allocated */
			rem_len = length - p->len;

			/* any remaining pbufs to be allocated? */
			while(rem_len > 0) {
				q = memp_malloc(MEMP_PBUF_POOL);

				if(q == NULL) {
					PBUF_POOL_IS_EMPTY();
					/* free chain so far allocated */
					pbuf_free(p);
					/* bail out unsuccesfully */
					return NULL;
				}

				q->type = type;
				q->flags = 0;
				q->next = NULL;
				/* make previous pbuf point to this pbuf */
				r->next = q;
				/* set total length of this pbuf and next in chain */
				LWIP_ASSERT("rem_len < max_u16_t", rem_len < 0xffff);
				q->tot_len = (u16_t)rem_len;
				/* this pbuf length is pool size, unless smaller sized tail */
				q->len = LWIP_MIN((u16_t)rem_len, PBUF_POOL_BUFSIZE_ALIGNED);
				q->payload = (void*)((u8_t*)q + SIZEOF_STRUCT_PBUF);
				LWIP_ASSERT("pbuf_alloc: pbuf q->payload properly aligned",
				            ((mem_ptr_t)q->payload % MEM_ALIGNMENT) == 0);
				LWIP_ASSERT("check p->payload + p->len does not overflow pbuf",
				            ((u8_t*)p->payload + p->len <=
				             (u8_t*)p + SIZEOF_STRUCT_PBUF + PBUF_POOL_BUFSIZE_ALIGNED));
				q->ref = 1;
				/* calculate remaining length to be allocated */
				rem_len -= q->len;
				/* remember this pbuf for linkage in next iteration */
				r = q;
			}

			/* end of chain */
			/*r->next = NULL;*/

			break;

		case PBUF_RAM:
			/* If pbuf is to be allocated in RAM, allocate memory for it. */
			p = (struct pbuf*)mem_malloc(LWIP_MEM_ALIGN_SIZE(SIZEOF_STRUCT_PBUF + offset) + LWIP_MEM_ALIGN_SIZE(length));

			if(p == NULL) {
				return NULL;
			}

			/* Set up internal structure of the pbuf. */
			p->payload = LWIP_MEM_ALIGN((void*)((u8_t*)p + SIZEOF_STRUCT_PBUF + offset));
			p->len = p->tot_len = length;
			p->next = NULL;
			p->type = type;

			LWIP_ASSERT("pbuf_alloc: pbuf->payload properly aligned",
			            ((mem_ptr_t)p->payload % MEM_ALIGNMENT) == 0);
			break;

		/* pbuf references existing (non-volatile static constant) ROM payload? */
		case PBUF_ROM:

		/* pbuf references existing (externally allocated) RAM payload? */
		case PBUF_REF:
			/* only allocate memory for the pbuf structure */
			p = memp_malloc(MEMP_PBUF);

			if(p == NULL) {
				LWIP_DEBUGF(PBUF_DEBUG | LWIP_DBG_LEVEL_SERIOUS,
				            ("pbuf_alloc: Could not allocate MEMP_PBUF for PBUF_%s.\n",
				             (type == PBUF_ROM) ? "ROM" : "REF"));
				return NULL;
			}

			/* caller must set this field properly, afterwards */
			p->payload = NULL;
			p->len = p->tot_len = length;
			p->next = NULL;
			p->type = type;
			break;

		default:
			LWIP_ASSERT("pbuf_alloc: erroneous type", 0);
			return NULL;
	}

	/* set reference count */
	p->ref = 1;
	/* set flags */
	p->flags = 0;
	LWIP_DEBUGF(PBUF_DEBUG | LWIP_DBG_TRACE, ("pbuf_alloc(length=%"U16_F") == %p\n", length, (void*)p));
	return p;
}


/**
 * Shrink a pbuf chain to a desired length.
 *
 * @param p pbuf to shrink.
 * @param new_len desired new length of pbuf chain
 *
 * Depending on the desired length, the first few pbufs in a chain might
 * be skipped and left unchanged. The new last pbuf in the chain will be
 * resized, and any remaining pbufs will be freed.
 *
 * @note If the pbuf is ROM/REF, only the ->tot_len and ->len fields are adjusted.
 * @note May not be called on a packet queue.
 *
 * @note Despite its name, pbuf_realloc cannot grow the size of a pbuf (chain).
 */
void
pbuf_realloc(struct pbuf* p, u16_t new_len)
{
	struct pbuf* q;
	u16_t rem_len; /* remaining length */
	s32_t grow;

	LWIP_ASSERT("pbuf_realloc: p != NULL", p != NULL);
	LWIP_ASSERT("pbuf_realloc: sane p->type", p->type == PBUF_POOL ||
	            p->type == PBUF_ROM ||
	            p->type == PBUF_RAM ||
	            p->type == PBUF_REF);

	/* desired length larger than current length? */
	if(new_len >= p->tot_len) {
		/* enlarging not yet supported */
		return;
	}

	/* the pbuf chain grows by (new_len - p->tot_len) bytes
	 * (which may be negative in case of shrinking) */
	grow = new_len - p->tot_len;

	/* first, step over any pbufs that should remain in the chain */
	rem_len = new_len;
	q = p;

	/* should this pbuf be kept? */
	while(rem_len > q->len) {
		/* decrease remaining length by pbuf length */
		rem_len -= q->len;
		/* decrease total length indicator */
		LWIP_ASSERT("grow < max_u16_t", grow < 0xffff);
		q->tot_len += (u16_t)grow;
		/* proceed to next pbuf in chain */
		q = q->next;
		LWIP_ASSERT("pbuf_realloc: q != NULL", q != NULL);
	}

	/* we have now reached the new last pbuf (in q) */
	/* rem_len == desired length for pbuf q */

	/* shrink allocated memory for PBUF_RAM */
	/* (other types merely adjust their length fields */
	if((q->type == PBUF_RAM) && (rem_len != q->len)) {
		/* reallocate and adjust the length of the pbuf that will be split */
		q = mem_realloc(q, (u8_t*)q->payload - (u8_t*)q + rem_len);
		LWIP_ASSERT("mem_realloc give q == NULL", q != NULL);
	}

	/* adjust length fields for new last pbuf */
	q->len = rem_len;
	q->tot_len = q->len;

	/* any remaining pbufs in chain? */
	if(q->next != NULL) {
		/* free remaining pbufs in chain */
		pbuf_free(q->next);
	}

	/* q is last packet in chain */
	q->next = NULL;

}

/**
 * Adjusts the payload pointer to hide or reveal headers in the payload.
 *
 * Adjusts the ->payload pointer so that space for a header
 * (dis)appears in the pbuf payload.
 *
 * The ->payload, ->tot_len and ->len fields are adjusted.
 *
 * @param p pbuf to change the header size.
 * @param header_size_increment Number of bytes to increment header size which
 * increases the size of the pbuf. New space is on the front.
 * (Using a negative value decreases the header size.)
 * If hdr_size_inc is 0, this function does nothing and returns succesful.
 *
 * PBUF_ROM and PBUF_REF type buffers cannot have their sizes increased, so
 * the call will fail. A check is made that the increase in header size does
 * not move the payload pointer in front of the start of the buffer.
 * @return non-zero on failure, zero on success.
 *
 */
u8_t
pbuf_header(struct pbuf* p, s16_t header_size_increment)
{
	u16_t type;
	void* payload;
	u16_t increment_magnitude;

	LWIP_ASSERT("p != NULL", p != NULL);

	if((header_size_increment == 0) || (p == NULL))
		return 0;

	if(header_size_increment < 0) {
		increment_magnitude = -header_size_increment;
		/* Check that we aren't going to move off the end of the pbuf */
		LWIP_ERROR("increment_magnitude <= p->len", (increment_magnitude <= p->len), return 1;);
	} else {
		increment_magnitude = header_size_increment;
#if 0
		/* Can't assert these as some callers speculatively call
		     pbuf_header() to see if it's OK.  Will return 1 below instead. */
		/* Check that we've got the correct type of pbuf to work with */
		LWIP_ASSERT("p->type == PBUF_RAM || p->type == PBUF_POOL",
		            p->type == PBUF_RAM || p->type == PBUF_POOL);
		/* Check that we aren't going to move off the beginning of the pbuf */
		LWIP_ASSERT("p->payload - increment_magnitude >= p + SIZEOF_STRUCT_PBUF",
		            (u8_t*)p->payload - increment_magnitude >= (u8_t*)p + SIZEOF_STRUCT_PBUF);
#endif
	}

	type = p->type;
	/* remember current payload pointer */
	payload = p->payload;

	/* pbuf types containing payloads? */
	if(type == PBUF_RAM || type == PBUF_POOL) {
		/* set new payload pointer */
		p->payload = (u8_t*)p->payload - header_size_increment;

		/* boundary check fails? */
		if((u8_t*)p->payload < (u8_t*)p + SIZEOF_STRUCT_PBUF) {
			LWIP_DEBUGF(PBUF_DEBUG | LWIP_DBG_LEVEL_SERIOUS,
			            ("pbuf_header: failed as %p < %p (not enough space for new header size)\n",
			             (void*)p->payload, (void*)(p + 1)));
			/* restore old payload pointer */
			p->payload = payload;
			/* bail out unsuccesfully */
			return 1;
		}

		/* pbuf types refering to external payloads? */
	} else if(type == PBUF_REF || type == PBUF_ROM) {
		/* hide a header in the payload? */
		if((header_size_increment < 0) && (increment_magnitude <= p->len)) {
			/* increase payload pointer */
			p->payload = (u8_t*)p->payload - header_size_increment;
		} else {
			/* cannot expand payload to front (yet!)
			 * bail out unsuccesfully */
			return 1;
		}
	} else {
		/* Unknown type */
		LWIP_ASSERT("bad pbuf type", 0);
		return 1;
	}

	/* modify pbuf length fields */
	p->len += header_size_increment;
	p->tot_len += header_size_increment;

	LWIP_DEBUGF(PBUF_DEBUG | LWIP_DBG_TRACE, ("pbuf_header: old %p new %p (%"S16_F")\n",
	            (void*)payload, (void*)p->payload, header_size_increment));

	return 0;
}

/**
 * Dereference a pbuf chain or queue and deallocate any no-longer-used
 * pbufs at the head of this chain or queue.
 *
 * Decrements the pbuf reference count. If it reaches zero, the pbuf is
 * deallocated.
 *
 * For a pbuf chain, this is repeated for each pbuf in the chain,
 * up to the first pbuf which has a non-zero reference count after
 * decrementing. So, when all reference counts are one, the whole
 * chain is free'd.
 *
 * @param p The pbuf (chain) to be dereferenced.
 *
 * @return the number of pbufs that were de-allocated
 * from the head of the chain.
 *
 * @note MUST NOT be called on a packet queue (Not verified to work yet).
 * @note the reference counter of a pbuf equals the number of pointers
 * that refer to the pbuf (or into the pbuf).
 *
 * @internal examples:
 *
 * Assuming existing chains a->b->c with the following reference
 * counts, calling pbuf_free(a) results in:
 *
 * 1->2->3 becomes ...1->3
 * 3->3->3 becomes 2->3->3
 * 1->1->2 becomes ......1
 * 2->1->1 becomes 1->1->1
 * 1->1->1 becomes .......
 *
 */
u8_t
pbuf_free(struct pbuf* p)
{
	u16_t type;
	struct pbuf* q;
	u8_t count;

	if(p == NULL) {
		LWIP_ASSERT("p != NULL", p != NULL);
		/* if assertions are disabled, proceed with debug output */
		LWIP_DEBUGF(PBUF_DEBUG | LWIP_DBG_LEVEL_SERIOUS,
		            ("pbuf_free(p == NULL) was called.\n"));
		return 0;
	}

	LWIP_DEBUGF(PBUF_DEBUG | LWIP_DBG_TRACE, ("pbuf_free(%p)\n", (void*)p));

	PERF_START;

	LWIP_ASSERT("pbuf_free: sane type",
	            p->type == PBUF_RAM || p->type == PBUF_ROM ||
	            p->type == PBUF_REF || p->type == PBUF_POOL);

	count = 0;

	/* de-allocate all consecutive pbufs from the head of the chain that
	 * obtain a zero reference count after decrementing*/
	while(p != NULL) {
		u16_t ref;
		SYS_ARCH_DECL_PROTECT(old_level);
		/* Since decrementing ref cannot be guaranteed to be a single machine operation
		 * we must protect it. We put the new ref into a local variable to prevent
		 * further protection. */
		SYS_ARCH_PROTECT(old_level);
		/* all pbufs in a chain are referenced at least once */
		LWIP_ASSERT("pbuf_free: p->ref > 0", p->ref > 0);
		/* decrease reference count (number of pointers to pbuf) */
		ref = --(p->ref);
		SYS_ARCH_UNPROTECT(old_level);

		/* this pbuf is no longer referenced to? */
		if(ref == 0) {
			/* remember next pbuf in chain for next iteration */
			q = p->next;
			LWIP_DEBUGF(PBUF_DEBUG | LWIP_DBG_TRACE, ("pbuf_free: deallocating %p\n", (void*)p));
			type = p->type;

			/* is this a pbuf from the pool? */
			if(type == PBUF_POOL) {
				memp_free(MEMP_PBUF_POOL, p);
				/* is this a ROM or RAM referencing pbuf? */
			} else if(type == PBUF_ROM || type == PBUF_REF) {
				memp_free(MEMP_PBUF, p);
				/* type == PBUF_RAM */
			} else {
				mem_free(p);
			}

			count++;
			/* proceed to next pbuf */
			p = q;
			/* p->ref > 0, this pbuf is still referenced to */
			/* (and so the remaining pbufs in chain as well) */
		} else {
			LWIP_DEBUGF(PBUF_DEBUG | LWIP_DBG_TRACE, ("pbuf_free: %p has ref %"U16_F", ending here.\n", (void*)p, ref));
			/* stop walking through the chain */
			p = NULL;
		}
	}

	PERF_STOP("pbuf_free");
	/* return number of de-allocated pbufs */
	return count;
}

/**
 * Count number of pbufs in a chain
 *
 * @param p first pbuf of chain
 * @return the number of pbufs in a chain
 */

u8_t
pbuf_clen(struct pbuf* p)
{
	u8_t len;

	len = 0;

	while(p != NULL) {
		++len;
		p = p->next;
	}

	return len;
}

/**
 * Increment the reference count of the pbuf.
 *
 * @param p pbuf to increase reference counter of
 *
 */
void
pbuf_ref(struct pbuf* p)
{
	SYS_ARCH_DECL_PROTECT(old_level);

	/* pbuf given? */
	if(p != NULL) {
		SYS_ARCH_PROTECT(old_level);
		++(p->ref);
		SYS_ARCH_UNPROTECT(old_level);
	}
}

/**
 * Concatenate two pbufs (each may be a pbuf chain) and take over
 * the caller's reference of the tail pbuf.
 *
 * @note The caller MAY NOT reference the tail pbuf afterwards.
 * Use pbuf_chain() for that purpose.
 *
 * @see pbuf_chain()
 */

void
pbuf_cat(struct pbuf* h, struct pbuf* t)
{
	struct pbuf* p;

	LWIP_ERROR("(h != NULL) && (t != NULL) (programmer violates API)",
	           ((h != NULL) && (t != NULL)), return;);

	/* proceed to last pbuf of chain */
	for(p = h; p->next != NULL; p = p->next) {
		/* add total length of second chain to all totals of first chain */
		p->tot_len += t->tot_len;
	}

	/* { p is last pbuf of first h chain, p->next == NULL } */
	LWIP_ASSERT("p->tot_len == p->len (of last pbuf in chain)", p->tot_len == p->len);
	LWIP_ASSERT("p->next == NULL", p->next == NULL);
	/* add total length of second chain to last pbuf total of first chain */
	p->tot_len += t->tot_len;
	/* chain last pbuf of head (p) with first of tail (t) */
	p->next = t;
	/* p->next now references t, but the caller will drop its reference to t,
	 * so netto there is no change to the reference count of t.
	 */
}

/**
 * Chain two pbufs (or pbuf chains) together.
 *
 * The caller MUST call pbuf_free(t) once it has stopped
 * using it. Use pbuf_cat() instead if you no longer use t.
 *
 * @param h head pbuf (chain)
 * @param t tail pbuf (chain)
 * @note The pbufs MUST belong to the same packet.
 * @note MAY NOT be called on a packet queue.
 *
 * The ->tot_len fields of all pbufs of the head chain are adjusted.
 * The ->next field of the last pbuf of the head chain is adjusted.
 * The ->ref field of the first pbuf of the tail chain is adjusted.
 *
 */
void
pbuf_chain(struct pbuf* h, struct pbuf* t)
{
	pbuf_cat(h, t);
	/* t is now referenced by h */
	pbuf_ref(t);
	LWIP_DEBUGF(PBUF_DEBUG | LWIP_DBG_TRACE, ("pbuf_chain: %p references %p\n", (void*)h, (void*)t));
}

/**
 * Dechains the first pbuf from its succeeding pbufs in the chain.
 *
 * Makes p->tot_len field equal to p->len.
 * @param p pbuf to dechain
 * @return remainder of the pbuf chain, or NULL if it was de-allocated.
 * @note May not be called on a packet queue.
 */
struct pbuf*
pbuf_dechain(struct pbuf* p)
{
	struct pbuf* q;
	u8_t tail_gone = 1;
	/* tail */
	q = p->next;

	/* pbuf has successor in chain? */
	if(q != NULL) {
		/* assert tot_len invariant: (p->tot_len == p->len + (p->next? p->next->tot_len: 0) */
		LWIP_ASSERT("p->tot_len == p->len + q->tot_len", q->tot_len == p->tot_len - p->len);
		/* enforce invariant if assertion is disabled */
		q->tot_len = p->tot_len - p->len;
		/* decouple pbuf from remainder */
		p->next = NULL;
		/* total length of pbuf p is its own length only */
		p->tot_len = p->len;
		/* q is no longer referenced by p, free it */
		LWIP_DEBUGF(PBUF_DEBUG | LWIP_DBG_TRACE, ("pbuf_dechain: unreferencing %p\n", (void*)q));
		tail_gone = pbuf_free(q);

		if(tail_gone > 0) {
			LWIP_DEBUGF(PBUF_DEBUG | LWIP_DBG_TRACE,
			            ("pbuf_dechain: deallocated %p (as it is no longer referenced)\n", (void*)q));
		}

		/* return remaining tail or NULL if deallocated */
	}

	/* assert tot_len invariant: (p->tot_len == p->len + (p->next? p->next->tot_len: 0) */
	LWIP_ASSERT("p->tot_len == p->len", p->tot_len == p->len);
	return ((tail_gone > 0) ? NULL : q);
}

/**
 *
 * Create PBUF_RAM copies of pbufs.
 *
 * Used to queue packets on behalf of the lwIP stack, such as
 * ARP based queueing.
 *
 * @note You MUST explicitly use p = pbuf_take(p);
 *
 * @note Only one packet is copied, no packet queue!
 *
 * @param p_to pbuf destination of the copy
 * @param p_from pbuf source of the copy
 *
 * @return ERR_OK if pbuf was copied
 *         ERR_ARG if one of the pbufs is NULL or p_to is not big
 *                 enough to hold p_from
 */
err_t
pbuf_copy(struct pbuf* p_to, struct pbuf* p_from)
{
	u16_t offset_to = 0, offset_from = 0, len;

	LWIP_DEBUGF(PBUF_DEBUG | LWIP_DBG_TRACE, ("pbuf_copy(%p, %p)\n",
	            (void*)p_to, (void*)p_from));

	/* is the target big enough to hold the source? */
	LWIP_ERROR("pbuf_copy: target not big enough to hold source", ((p_to != NULL) &&
	           (p_from != NULL) && (p_to->tot_len >= p_from->tot_len)), return ERR_ARG;);

	/* iterate through pbuf chain */
	do {
		LWIP_ASSERT("p_to != NULL", p_to != NULL);

		/* copy one part of the original chain */
		if((p_to->len - offset_to) >= (p_from->len - offset_from)) {
			/* complete current p_from fits into current p_to */
			len = p_from->len - offset_from;
		} else {
			/* current p_from does not fit into current p_to */
			len = p_to->len - offset_to;
		}

		MEMCPY((u8_t*)p_to->payload + offset_to, (u8_t*)p_from->payload + offset_from, len);
		offset_to += len;
		offset_from += len;
		LWIP_ASSERT("offset_to <= p_to->len", offset_to <= p_to->len);

		if(offset_to == p_to->len) {
			/* on to next p_to (if any) */
			offset_to = 0;
			p_to = p_to->next;
		}

		LWIP_ASSERT("offset_from <= p_from->len", offset_from <= p_from->len);

		if(offset_from >= p_from->len) {
			/* on to next p_from (if any) */
			offset_from = 0;
			p_from = p_from->next;
		}

		if((p_from != NULL) && (p_from->len == p_from->tot_len)) {
			/* don't copy more than one packet! */
			LWIP_ERROR("pbuf_copy() does not allow packet queues!\n",
			           (p_from->next == NULL), return ERR_VAL;);
		}

		if((p_to != NULL) && (p_to->len == p_to->tot_len)) {
			/* don't copy more than one packet! */
			LWIP_ERROR("pbuf_copy() does not allow packet queues!\n",
			           (p_to->next == NULL), return ERR_VAL;);
		}
	} while(p_from);

	LWIP_DEBUGF(PBUF_DEBUG | LWIP_DBG_TRACE, ("pbuf_copy: end of chain reached.\n"));
	return ERR_OK;
}

/**
 * Copy (part of) the contents of a packet buffer
 * to an application supplied buffer.
 *
 * @param buf the pbuf from which to copy data
 * @param dataptr the application supplied buffer
 * @param len length of data to copy (dataptr must be big enough). No more
 * than buf->tot_len will be copied, irrespective of len
 * @param offset offset into the packet buffer from where to begin copying len bytes
 * @return the number of bytes copied, or 0 on failure
 */
u16_t
pbuf_copy_partial(struct pbuf* buf, void* dataptr, u16_t len, u16_t offset)
{
	struct pbuf* p;
	u16_t left;
	u16_t buf_copy_len;
	u16_t copied_total = 0;

	LWIP_ERROR("pbuf_copy_partial: invalid buf", (buf != NULL), return 0;);
	LWIP_ERROR("pbuf_copy_partial: invalid dataptr", (dataptr != NULL), return 0;);

	left = 0;

	if((buf == NULL) || (dataptr == NULL)) {
		return 0;
	}

	/* Note some systems use byte copy if dataptr or one of the pbuf payload pointers are unaligned. */
	for(p = buf; len != 0 && p != NULL; p = p->next) {
		if((offset != 0) && (offset >= p->len)) {
			/* don't copy from this buffer -> on to the next */
			offset -= p->len;
		} else {
			/* copy from this buffer. maybe only partially. */
			buf_copy_len = p->len - offset;

			if(buf_copy_len > len)
				buf_copy_len = len;

			/* copy the necessary parts of the buffer */
			MEMCPY(&((char*)dataptr)[left], &((char*)p->payload)[offset], buf_copy_len);
			copied_total += buf_copy_len;
			left += buf_copy_len;
			len -= buf_copy_len;
			offset = 0;
		}
	}

	return copied_total;
}

/**
 * Copy application supplied data into a pbuf.
 * This function can only be used to copy the equivalent of buf->tot_len data.
 *
 * @param buf pbuf to fill with data
 * @param dataptr application supplied data buffer
 * @param len length of the application supplied data buffer
 *
 * @return ERR_OK if successful, ERR_MEM if the pbuf is not big enough
 */
err_t
pbuf_take(struct pbuf* buf, const void* dataptr, u16_t len)
{
	struct pbuf* p;
	u16_t buf_copy_len;
	u16_t total_copy_len = len;
	u16_t copied_total = 0;

	LWIP_ERROR("pbuf_take: invalid buf", (buf != NULL), return 0;);
	LWIP_ERROR("pbuf_take: invalid dataptr", (dataptr != NULL), return 0;);

	if((buf == NULL) || (dataptr == NULL) || (buf->tot_len < len)) {
		return ERR_ARG;
	}

	/* Note some systems use byte copy if dataptr or one of the pbuf payload pointers are unaligned. */
	for(p = buf; total_copy_len != 0; p = p->next) {
		LWIP_ASSERT("pbuf_take: invalid pbuf", p != NULL);
		buf_copy_len = total_copy_len;

		if(buf_copy_len > p->len) {
			/* this pbuf cannot hold all remaining data */
			buf_copy_len = p->len;
		}

		/* copy the necessary parts of the buffer */
		MEMCPY(p->payload, &((char*)dataptr)[copied_total], buf_copy_len);
		total_copy_len -= buf_copy_len;
		copied_total += buf_copy_len;
	}

	LWIP_ASSERT("did not copy all data", total_copy_len == 0 && copied_total == len);
	return ERR_OK;
}

/**
 * Creates a single pbuf out of a queue of pbufs.
 *
 * @remark: The source pbuf 'p' is not freed by this function because that can
 *          be illegal in some places!
 *
 * @param p the source pbuf
 * @param layer pbuf_layer of the new pbuf
 *
 * @return a new, single pbuf (p->next is NULL)
 *         or the old pbuf if allocation fails
 */
struct pbuf*
pbuf_coalesce(struct pbuf* p, pbuf_layer layer)
{
	struct pbuf* q;
	err_t err;

	if(p->next == NULL) {
		return p;
	}

	q = pbuf_alloc(layer, p->tot_len, PBUF_RAM);

	if(q == NULL) {
		/* @todo: what do we do now? */
		return p;
	}

	err = pbuf_copy(q, p);
	LWIP_ASSERT("pbuf_copy failed", err == ERR_OK);
	pbuf_free(p);
	return q;
}
